1. Field of the Invention
This invention relates to a toner used in image recording processes such as electrophotography, electrostatic printing and toner jet recording.
2. Description of the Related Art
In recent years, because of progress in computers and multimedia, it is sought to provide means which can reproduce high-definition images in a broad field extending from offices to homes. Accordingly, it is needed to provide means which can reproduce high-quality images without being affected by any environmental variations even in a cold and dry environment and in a high-temperature and high-humidity environment.
In general, most toners are those to the base particle surfaces of which an inorganic fine powder or fine particles formed of resin has or have been added. In virtue of the presence of such particles, performance such as chargeability or fluidity of toners is improved. However, where two or more different kinds of inorganic fine powders are used, only one of the inorganic fine powders for example may come off, or come buried in, the base particles as a result of long-term continuous service to make it difficult for the toners to retain the fluidity, charging stability, environmental stability and so forth they have at the initial stage.
Accordingly, studies are made on what is called composite particles, which are made up by using two or more compounds. Such toners making use of composite particles are known to be effective in maintaining toner performance over a long period of time because the properties of the compounds used are individually brought out and the charging is stably maintained even under conditions such as long-term continuous service and environmental variations. For example, a technique is proposed in which silica composite particles containing aluminum, boron or titanium are used to make toners retain initial-stage charge characteristics even in their long-term continuous service (see, e.g., Japanese patent Nos. 03587671 and 03587672). A technique is also proposed in which the content of titania in silica titania composite particles and BET specific surface area thereof are specified so as to make toners improved in their environmental stability (see, e.g., Japanese Patent Application Laid-open No. 2006-306651). Meanwhile, a technique is still also proposed in which the content of titania in silica titania composite particles and the particle diameter of the silica titania composite particles are specified so as to make toners retain fluidity in their long-term leaving (see, e.g., Japanese Patent Application Laid-open No. 2008-112046).
The above Japanese patent Nos. 03587671 and 03587672 report that toners can well retain charge characteristics in their long-term continuous service. However, the composite particles used therein have an insufficient hydrophobicity, and you must worry about a decrease in charge characteristics of toners that is due to their continuous service or leaving in a high-temperature and high-humidity environment.
The above Japanese Patent Application Laid-open No. 2006-306651 reports that the titania in silica titania composite particles is in a content of 50% by mass or more and this promises superior environmental stability and charging stability. However, you must worry about a lowering of fluidity and chargeability of toners in their long-term continuous service.
The above Japanese Patent Application Laid-open No. 2008-112046 reports that the titania in silica titania composite particles is in a large content and also the particle diameter of the silica titania composite particles are specified, and this enables toners to retain fluidity in their long-term leaving. However, you must worry about a lowering of fluidity and chargeability of toners in their long-term continuous service.